Radio receiving circuit



June 11, 1929. N, H, SLAUGHTER 1.7177174 mmo macmvme cmcpm Filed Sept.6, 1924 lnrenfar: Nugemhf filaug/zfer by I A/fy.

Patented June 11, 1929.

UNITED STATES room 3.

mOTBIO COMPANY, INCORPORATED,

NEW YORK.

SLAUGHTER, MOUNTAIN LAKES, NEW JERSEY, ASSIGNOB TO WESTERN OF NEW YORK,N. Y., A OOBPOBA'L'I ON'OF BADIO RECEIVING OIBOU 1'1.

Application fled September This invention relates to radio receivingcircuits and has .for its principal object to provide a receiving setall variable elements of which are capab e of adjustment for receptionof waves of difierent lengths by means of a single control element.

Another object of this invention is to provide a receiving set adaptedto be used with various aerials without changing the dial settings.

A further object is to provide in a receiving set, that the naturalperiod of a tuned antenna circuit is not materially altered by a changein serials.

A still further object is to increase the shar ness of tuning of thecircuit.

0 er objects and advantages will be apparent from the followingspecification and claims.

These objects are accom lished by means of a small condenser insertebetween the aerial and tuned primary circuit constituting a selectiveelement of the receiver.

Figs. 1, 2 and 3 show diagrammatically, g circuits embodying theinvention inwhic corresponding parts are designated by the samereference numerals.

In all figuresi condenser 1 is-interposed between the aeria and primarycircuit 2 which may be tuned by variable condenser 16. The

maximum capacity of the condenser 1 is of the order of 75 mmf. which issmall compared to that of the other condensers or elements of thecircuit involving capacity to-ground capacity and condenser 16 in theprimary circuit 2, which would be I of 500 mmf. .The condenser 1 may beas small as 50 mmf. it being understood that the values herein assignedare in an apparatus suitable 40 for receiving present broadcast messageson wave lengths of from 200 to 600 meters and that the values for. otherwave lengths will difier accordingly.

A secondary circuit 3 consisting of inductance 11 and secondary tuningcondenser 12 is tuned to the same fre uency as the circuit 2 and isloosely couple thereto either by electromagneticor electrostatic meanswhich may be made variable, if desired, for the purpose of adjusting thecoupling between the circuits 2 and 3. v 1 As indicated on the drawings,the condensers 12 and 16 are to be varied simultaneously by a singlecontrol element and in order to such as the aerial-v of the order 8,1924. Serial No. 738,241.

effect this result it is needful that 'theybe shunted during the tuningoperation by effective capacities of equal value. The condense rs 12 and16 may in general, be of any variable type each being identical indesign with the 0 er.

Various means of con ling the rimary and secondary circuits are s own inI igs. 1 2 and 3. In Fig. 1, a. series ca ificity coupling is obtained bcondenser 7 w 'ch is preferably variable. 11 Fig. 2, a shunt ca acitycouphng is shown by means of con enser 8 between primary circuit 2 andsecondary circuit 3. In Fig. 3, primary circuit 2'is cou led to Isecondary circuit 3 by receivin trans ormer 9 which may be made adjustabe for varying the coupling. Any other means of coupling the circuits mayfrom the spirit of the invention.

A vacuum tube detector 4, provided with the usual stopping condensershunted by a high resistance in the grid circuit, is connected acrossthe circuit 3. The anode cirbe used without departing cuit 5 contains atelephone receiver 6 which typifies any desired receiving apparatus.

A small adjustable condenser 10 is connected in parallel to thesecondary tuning condenser. that the combined capacity of condenser 10,input capacity ofvacuurn tube 4, and dis tributedcapacity of thesecondary coil 11 and the wiring 1s of the order of 50 mi.

A single or plural stage am lifier may be inserted in tandem between t etube 4 and receiver 5 in any one of. several well known manners, inwhich case the input capacity of the amplifier is taken into account inthe same manner as that of the detector-when there is no amplifier.

The operation and advantages of this circuit may be explained asfollows: The'primary circuit contains cagacity due to the tu'ningcondenser and also ue to the aerial, operatin secon ary circuit has twocapacities in arallel in a similar manner due to the secon ary tun incondenser and distributed capacity of coi s, wiring and tube. In orderto permit equal variation of both primary and secondary tuningcondensers so that tuningcan be efiectively accomplished by a singlecontrol without redesigning for each sli htly difierent aerial, theefiective values of the capacities in shunt must be made by varying themThe, condenser 10 is adjusted so.

equal. This was previously difiicult of accomplishment as theaerial-to-ground capacity was varied each time the set was used ondifferent aerials and was of a large magnltude relative to thedistributed capacity in the secondary circuit.

In accordance with this invention, the secondary capacity is adjusted toany desired amount by a small condenser 10 in parallel to thetuningcondenser. This condenser is adjusted so that the combinedcapacity resulting from the vacuum tube wiring and condenser itself isapproximately 50 mmf., an amount large enou h to permit of accurateadjustment and suficiently small so that the minimum capacity of thesecondary circuit may be made as small as desired in tuning. The primaryis adjusted in an analogous manner by inserting a condenser 1 of 75 mmf.maximum capacity in series with the aer1al. By varying this condenser,the effective capacity of the aerial to ground and condenser 1 in seriesmay be made any des1red amount less than 75 mmf, the maximum capacity ofcondenser 1. This will be the case irrespective of the type of aerialused. 0 If this capacity is made equal to the minimum secondary capacityor about 50 mmf. the primary and secondary tuning condensers may bevaried simultaneously by the same control means and the circuits willalways be tuned to the same frequency.

Should the distributed capacity of the secondary circuit be 50 mmf. orgreater, condenser 10 may be omitted. In case this capacity should begreater than 75 mmf. condenser 1 must have a larger maximum capacity toproperly balance the circuits. It should be understood that the valuesherein used are only examples. The actual values of condensers 1 and 10must be determined in accordance with the particular ty e of receiversand the use to which it is to be put.

In practice, the small condenser 10 may be adjusted in the factory andboth tuning con- .densers connected to the same knob and dial. The setis then connected to an aerial and maximum signal strength obtained byadjusting condenser 1. After this is once adjusted for-a given aerial,it will not thereafter need to be changed as the circuits are then ofequal capacity and the single control knob will tune in all signalswithin the rangev of the receiver.

Condenser 1 also materially increases the sharpness of tuning of theprimary circuit as the loose coupling between the aerial and primarycircuit caused thereby greatly reduces the damping effect of the aerialresistance on the primary circuit.

It is known that condensers have been used in series with the aerial forpurposes of tunm but the instruments and purpose are consi ered to beentirely different than as herein set forth. The condenser 1 is toosmall to be large that of any value in tuning and, in fact, would notvary the period of the aerial to ground circuit to any appreciableextent. Condensers such as previously used in tuning were so they couldnot function in accordance with this invention. They were not ofsufiiciently high impedance to insure absence 'ofinteraction between theaerial and tuned primary. The tuning of the primary was affected by thesize of the aerial and the sharpness of tuning was affected by theresistance of the aerial.

Although shown as applied to particular,

circuitsit is to be understood that the invention is not limited in itsapplication to these particular circuits but only in accordance with thespirit of the invention as defined in the claims.

-What is claimed is:

1. In a radio receivingcircuit comprising an aerial and tuning means, acondenser of the order of 75mmf. interposed between said aerial and saidtuning means to minimize the effect of the aerial on the tuning of theantenna circuit and a resonant circuit coupled to said tuning meanshaving a total minimum capacity substantially e ual to the combinedcapacity of said aerial and said condenser. V

2. In combination, two resonant circuits, an element having capacity toground, means for tuning both said circuits in a single operation, and apath between said element and one of said circuits including a capacityfor minimizing the effect of said capacity to ground on said circuits.

3. In combination, two coupled resonant circuits, means for tunin saidcircuits in one operation, an element having capacity to groundconnected to one of said circuits, an-

other element having material capacity connected to the other of saidcircuits, and supplementary means associated with the circuit havingcapacity to ground for equalizing the capacity of said elements wherebysaid circuits may be maintained in resonance at the same frequency.

4. In combination two coupled resonant circuits, means for tuning saidcircuits in one operation, one of said circuits including an elementhaving material inherent capacity and the other of said circuits beingadapted to be connected to any one of several elements having differentmaterial capacities,

and means to reduce the influence of saidelements of difi'erentcapacities on the tuning of the connected circuit comprising anadditional capacity adapted to-be included in the connection to saidelements. of. difi'erent capacities.

5. In a radio receiving circuit comprising an aerial and primary andsecondary tuning means, means comprising a small condenser connectedacross said secondary tuning means to adjust the minimum secondarycapacity to a finite value and means comprising a small condenserconnected between the aerial and primary tuning means to adjust theantenna capacity to the same finite value 5 so that equal changes in theprimary and secondary tuning meansv will produce equal changes in frequency of the respective circuits whereby they may be controlled by asingle means.

In Witness whereof, I hereunto subscribe 10 myname this 5th day ofSeptember, A. D. 192

NUGENT H. SLAUGHTER.

